Animal fats and margarine consumption in the United States have been largely replaced by palm oil, a plant-based oil that has similar cooking properties, but may not be as environmentally-friendly as commonly believed, argues a researcher in this week's issue of Nature.

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José Bonner, a biologist at Indiana University, analyzed fat consumption trends in the United States and compared the chemical make-up of palm oil, lard, and margarine. He finds that chemically, the three are near substitutes for one another. Accordingly, health fads and the rise in cheap palm oil has led to it replacing margarine, which originally supplanted lard, when it fell out of fashion due to health concerns.

"The popularity of butter and lard declined in the 1940s and 1950s, giving way to margarine. This shift was fueled by the belief that vascular health could be improved by switching from saturated animal fats to unsaturated plant oils. Margarine fell from grace around 1990, when it was discovered that plant-oil solidification produces metabolically harmful trans-fat," he writes. "The physical-chemical properties of lard make it ideal for baking, and palm oil is an effective substitute because its chemical composition is almost identical."

The problem, says Bonner, is palm oil is neither as healthy or environmentally-friendly as some believe. Over the past 20 years large swathes of rainforest across Malaysia and Indonesia have been cleared for oil palm plantations. The industry is now expanding in other parts of Asia, Central and South America, West and Central Africa, and even Madagascar.